A disc-shaped optical data recording medium has a signal recording layer for reading and/or writing data using light, and a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer. The optical data recording medium includes a protrusion projecting from a surface of the transparent protective layer on a light-incidence surface side to which light is emitted to the signal recording layer. The protrusion is disposed in an area between a center hole and a clamping area where the optical data recording medium is held when reading and/or writing data in the signal recording layer.
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1. An optical disc with a center hole, the optical disc comprising:
a signal substrate;
a signal recording layer for storing data;
a transparent protective layer disposed over said signal recording layer; and
a protrusion projecting from a surface of said transparent protective layer, wherein
a signal area of the optical disc is located over said signal recording layer,
a clamping area of the optical disc is located between the signal area and the center hole,
said protrusion is disposed at an area of the optical disc between the center hole and the clamping area,
a material of said protrusion is different from a material of said transparent protective layer, and
said transparent protective layer is disposed in a first area of said signal substrate, and said protrusion is disposed in a second area of said signal substrate which is different and located distantly from the first area.
2. An optical disc according to
3. An optical disc according to
4. An optical disc according to
5. An optical disc according to
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This application is a divisional application of application Ser. No. 10/655,135, filed Sep. 5, 2003 now U.S. Pat. No. 7,065,776.
1. Field of the Invention
The present invention relates to a disc-shaped optical data recording medium having a signal recording layer for recording and/or playing information by emitting a light beam thereto, and a transparent protective layer 10 μm to 200 μm thick disposed over the signal recording layer. The invention also relates to a method for manufacturing this optical data recording medium, and to a method for clamping the optical data recording medium.
2. Description of Related Art
Optical discs are known and widely used as a high capacity data storage medium for high density recording and playback of information using a laser beam. These optical discs are broadly categorized as read-only, incrementally writable (multisession), and rewritable. Typical of read-only discs are Compact Discs (CDs) storing audio content and Laser Discs storing video content such as movies. Both incrementally writable (multisession) and rewritable media are widely used in the computer industry, for example, for storing text documents and still image files.
These optical discs typically have a data layer disposed to one main side of a 1.2 mm thick transparent substrate. A protective overcoat is then applied to the data layer, or a protective disc identical to the transparent substrate is bonded by adhesive to the data layer. See, for example, Japanese Laid-Open Patent Publication No. 2001-093193, paragraph [0015] and FIG. 1, and Japanese Laid-open Patent Publication No. 2002-042376, paragraph [0019] and FIG. 1.
Development and introduction of Digital Versatile Discs (DVD), a high capacity optical disc medium, has made it practical for even end-users to record moving picture content (such as movies and video) together with audio to an optical disc. High density media such as DVD have been achieved by using a shorter wavelength laser and an objective lens with a large numeric aperture (NA). However, shortening the beam wavelength and increasing the NA also reduce the tolerance for tilt, the inclination of the disc to the direction of laser beam emission.
Tolerance for tilt can be improved by using a thinner substrate. With DVD media this means, for example, using a 0.6 mm thick substrate assuming a 650 nm laser and 0.60 NA. Because a 0.6 mm thick substrate is mechanically weak and would thus increase tilt, DVD discs have two such substrates bonded together with the data recording surfaces on the inside between the substrates.
By using this laminated structure a transparent reflective layer of gold or silicon, for example, is formed on the data recording surface of one of the two substrates, and a conventional reflective layer of aluminum, for example, is formed on the data recording surface of the other substrate. The substrates are then bonded together with these data recording surfaces facing each other on the inside, resulting in a single-sided, double-layer DVD that can be read from one side of the disc, that is, from the side of the substrate having the transparent reflective layer over the data recording layer. Rewritable DVD media with a similar double-layer construction are also available, but the data recording surface in this case is a rewritable thin-film recording layer instead of a metal mirror layer.
Using a blue-purple laser with an approximately 400 nm wavelength has also been proposed as a way to achieve even higher recording densities. One method uses an approximately 0.1 mm thick transparent protective layer on the read/write side and forms an ultrafine laser spot using an approximately 0.85 NA lens for signal reading and/or writing. The transparent layer can be formed with the following two methods.
(A) Bonding a transparent substrate slightly less than 0.1 mm thick to the signal surface side of a 1.1 mm thick signal substrate using adhesive.
(B) Coating the signal surface side of a 1.1 mm thick signal substrate with an approximately 0.1 mm thick transparent resin layer.
In method (A) a polycarbonate sheet manufactured by casting, for example, is used as the transparent substrate. Thickness variation in such cast sheets is minimal at approximately +/−1 μm. The thickness of the adhesive used to bond this polycarbonate sheet to the signal substrate is also thin and can be easily formed to a uniform thickness. As a result, a transparent protective layer with uniform thickness can be formed on the recording/playback side of the disc.
With method (B) it is difficult to form a uniformly thick coating because of the thickness of the transparent resin, but a low cost, high density optical disc can be achieved because it is not necessary to use sheets manufactured in a high cost casting process.
A problem with high density optical discs is that the surface of the transparent protective layer is easily scratched, and scratches can easily cause a loss of servo control. Increasing the mechanical strength of the transparent protective layer itself increases the film thickness, and is not suited for high density recording. It is therefore difficult to protect the surface from scratching while keeping the transparent protective layer thin.
The data transfer rate during recording and playback is higher with high density optical discs than conventional CD and DVD media, and the disc therefore spins faster. Imbalances in the shape and weight of the disc relative to the spindle hole can therefore increase the load on the rotating spindle (motor).
In addition, high speed rotation of these high density optical discs also requires higher disc clamping force than CD and DVD discs.
The present invention is therefore directed to solving these three problems, and an object of the invention is to provide an optical data recording medium having surface protrusions for protecting the transparent protective layer and reducing the load on the motor during disc rotation, and enabling higher disc clamping force to be applied to the optical data recording medium.
To achieve the above objects an optical data recording medium with a signal recording layer for reading and/or writing data using light, and a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, comprises a protrusion projecting from the surface of the transparent protective layer on the light-incidence surface side to which light is emitted to the signal recording layer in an area between a center hole and a clamping area where the optical data recording medium is held when reading and/or writing data in the signal recording layer.
Because this protrusion is on the inside circumference side of the clamping area, the protrusion will not interfere (collide) with the optical head. Furthermore, when the optical data recording medium is placed on a flat surface with the transparent protective layer side facing the flat surface, the protrusion keeps the transparent protective layer off the flat surface and thereby prevents scratching the transparent protective layer.
The load imposed on the rotating spindle (motor) caused by a weight imbalance in the protrusion is also reduced because the protrusion is located near the center spindle hole.
The protrusion is preferably disposed separated at least 0.1 mm in the radial direction from an outside edge of the center hole. This configuration prevents the protrusion from interfering with the center cone used to hold the optical data recording medium at the spindle hole in the disc recording and playback drive, and thereby enables stable clamping of the optical data recording medium.
In another aspect of the invention a disc-shaped optical data recording medium with a signal recording layer for reading and/or writing data using light, and a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, is characterized by having a clamping area on the outside of the center hole in the radial direction for holding the optical data recording medium when reading or recording data in the signal recording layer; a signal area on the outside of the clamping area in the radial direction for recording or reading data in the signal recording layer; and a protrusion projecting from the surface of the transparent protective layer in an area disposed between the clamping area and signal area on the light-incidence side of the signal recording layer to which light is emitted for reading and/or writing information.
When this optical data recording medium is placed on flat surface with the transparent protective layer thereof facing the flat surface, the proximity of the protrusion to the signal area keeps the transparent protective layer separated from the flat surface and thereby provides excellent protection for the transparent protective layer.
Preferably, the protrusion is disposed to an area within 2 mm to the outside in the radial direction from the outside circumference edge of the clamping area.
Interference between the protrusion and the optical head is thus further prevented because the protrusion is sufficiently separated from the signal area.
A disc-shaped optical data recording medium having a signal recording layer for reading and/or writing data using light, and a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, according to a further aspect of the invention is characterized by a clamping area on the outside of the center hole in the radial direction for holding the optical data recording medium when reading or recording the signal recording layer; a signal area on the outside of the clamping area in the radial direction for recording or reading data in the signal recording layer; and a protrusion projecting from the surface of the transparent protective layer in the clamping area on the light-incidence side of the signal recording layer to which light is emitted for reading and/or writing information.
This optical data recording medium is clamped on both sides of the protrusion in the clamping area. There is therefore no interference (collision) with the optical head, and the transparent protective layer will not be scratched when the disc is placed on a flat surface with the transparent protective layer facing said flat surface because the protrusion disposed to the same side of the disc keeps the transparent protective layer raised above the flat surface.
Further, greater clamping force can be applied and the disc can be spun stably, assuring good signal quality. The load imposed on the rotating spindle (motor) caused by a weight imbalance in the protrusion is also reduced because the protrusion is located near the center spindle hole.
Preferably, the protrusion projects to a height of 0.05 mm to 0.5 mm from the surface of the transparent protective layer. The transparent protective layer will therefore not be scratched when the disc is placed on a flat surface with the transparent protective layer facing the flat surface because the protrusion projects sufficiently above the disc surface on the same side to keep the transparent protective layer from contacting the flat surface. Scratch-prevention and cost are further improved if the protrusion height is further preferably 0.1 mm to 0.3 mm from the surface of the transparent protective layer.
Yet further preferably, the wavelength of light for recording or reading information in the signal recording layer is 410 nm or less so that a small beam spot enabling high density recording and playback can be achieved.
Another aspect of the present invention is a manufacturing method for a disc-shaped optical data recording medium having a signal recording layer for reading and/or writing data using light, a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, and a protrusion projecting from the surface of the transparent protective layer on the light-incidence surface side to which light is emitted to the signal recording layer. This manufacturing method has steps for: preparing a first die with a cavity corresponding to the protrusion, and a second die corresponding to the first die; disposing and closing the first die and second die together; injecting resin between the first die and second die; curing the resin to form a resin molding having the protrusion; and opening the first die and second die, and removing the cured resin molding.
In another manufacturing method for a disc-shaped optical data recording medium having a signal recording layer for reading and/or writing data using light, a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, and a protrusion projecting from the surface of the transparent protective layer on the light-incidence surface side to which light is emitted to the signal recording layer, a substrate for the optical data recording medium is formed by injection molding using a die having a cavity corresponding to the protrusion, and the protrusion is simultaneously formed on the substrate.
These manufacturing methods for an optical data recording medium according to the present invention provide a cavity corresponding to the desired shape of the protrusion in a die, and then introduce molten resin to the mold and apply pressure in an injection molding process. This produces a substrate with a signal pattern transferred from the stamper in the mold and a protrusion simultaneously formed to the substrate surface, thereby improving mass production of the optical data recording medium.
In another aspect of a manufacturing method for a disc-shaped optical data recording medium having a signal recording layer for reading and/or writing data using light, a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, and a protrusion projecting from the surface of the transparent protective layer on the light-incidence surface side to which light is emitted to the signal recording layer, the protrusion is formed on the optical data recording medium by bonding thereto a part in the shape of the protrusion.
By thus bonding parts forming the desired shape of the protrusion to the disc surface, this optical data recording medium manufacturing method can easily form the protrusion at a desired location on the disc, thereby improving mass production.
In another aspect of a manufacturing method for a disc-shaped optical data recording medium having a signal recording layer for reading and/or writing data using light, a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, and a protrusion projecting from the surface of the transparent protective layer on the light-incidence surface side to which light is emitted to the signal recording layer, the protrusion is formed on the optical data recording medium by dripping a liquid material onto the optical data recording medium and curing the liquid material in the shape of the protrusion.
This manufacturing method can easily produce protrusions of the desired shape at the desired location of the disc surface by simply changing how the liquid material is dripped onto the substrate. Little time is also needed to form the protrusions, and optical data recording media having protrusions according to the present invention can therefore be manufactured at low cost.
In another aspect of a manufacturing method for a disc-shaped optical data recording medium having a signal recording layer for reading and/or writing data using light, a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer, and a protrusion projecting from the surface of the transparent protective layer on the light-incidence surface side to which light is emitted to the signal recording layer, the protrusion is formed on the optical data recording medium by a screen printing process using a screen having the desired shape of the protrusion.
This manufacturing method can easily produce protrusions of the desired shape at the desired location of the disc surface by simply changing the pattern of the protrusions in the screen. Little time is therefore needed to form the protrusions, and optical data recording media having protrusions according to the present invention can therefore be manufactured at low cost.
The material used to make the parts bonded to the optical data recording medium surface, and the material of the protrusions formed by screen printing, in the optical data recording medium manufacturing methods described above is preferably a resin. This makes materials handling simple, enables using low cost materials, and improved productivity. The resin is further preferably a UV-cure resin, a thermosetting resin, or a pressure-sensitive adhesive. Each of these materials is inexpensive and easily procured.
Further preferably, the protrusion is disposed in an area between the center hole and a clamping area where the optical data recording medium is held for reading and/or writing data in the signal recording layer.
This configuration locates the protrusion on the optical data recording medium surface on the inside circumference side of the clamping area. The protrusion therefore does not interfere (collide) with the optical head, and the transparent protective layer will not be scratched when the disc is placed on a flat surface with the transparent protective layer facing said flat surface because the protrusion disposed to the same side of the disc prevents the transparent protective layer from touching the flat surface. Disc reliability can therefore be assured for a long time.
Yet further preferably, the protrusion is disposed in an area between the clamping area for holding the optical data recording medium when reading or recording data in the signal recording layer, and the signal area for recording or reading data in the signal recording layer.
Yet further preferably, the protrusion is disposed to an area within 2 mm to the outside in the radial direction from the outside circumference edge of the clamping area. In this case the optical data recording medium assures no interference between the protrusion and optical head regardless of the recording and playback device in which it is used.
Yet further preferably, the protrusion is disposed in the clamping area for holding the optical data recording medium when reading or recording data in the signal recording layer.
Because the disc in this case is clamped on both sides of the protrusion, the protrusion is prevented from interfering with the optical head while also protecting the transparent protective layer. Greater clamping force can also be applied to the optical data recording medium.
Yet further preferably, the protrusion is formed to a height of 0.05 mm to 0.5 mm from the surface of the transparent protective layer. Because the protrusion thus projects sufficiently from the transparent protective layer surface with this configuration, the transparent protective layer will not be scratched when the disc is placed on a flat surface because the transparent protective layer is prevented from touching said flat surface by the protrusion. A more dependable optical data recording medium can therefore be manufactured.
Scratch-prevention and cost are further improved if the protrusion height is further preferably 0.1 mm to 0.3 mm from the surface of the transparent protective layer.
Another aspect of the present invention is a clamping method for a disc-shaped optical data recording medium having a signal recording layer for reading and/or writing data by emitting light using an optical head with a 0.7 to 0.9 numeric aperture, and a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer. The optical data recording medium has a clamping area on the outside of the center hole in the radial direction for holding the optical data recording medium when reading or recording data in the signal recording layer, a signal area on the outside of the clamping area in the radial direction for recording or reading data in the signal recording layer, and a protrusion projecting from the surface of the transparent protective layer in the clamping area on the light-incidence side of the signal recording layer to which light is emitted for reading and/or writing information. The clamping method holds the optical data recording medium on both sides of the protrusion when recording or reading data in the signal recording layer of the optical data recording medium.
By holding the optical data recording medium on both sides of the protrusion, this disc clamping method can apply greater clamping force, the disc can be spun stably, and good signal quality can be achieved.
Preferably, the area for clamping on both sides of the protrusion on the light incidence side is in a radial area with a radius of 11 mm to 16.5 mm.
Yet further preferably, the optical data recording medium is clamped by both holding the optical data recording medium on both sides of the protrusion on the light incidence side and holding the protrusion.
By thus clamping the disc in two areas on opposite sides of the protrusion and by applying pressure directly to the protrusion, even greater clamping force can be applied.
With an optical data recording medium according to the present invention the protrusion will not interfere (collide) with the optical head and the transparent protective layer is protected from scratches when the disc is placed transparent protective layer-side down on a flat surface because the protrusion prevents the transparent protective layer from touching the flat surface.
Furthermore, the load on the rotating spindle (motor) caused by a weight imbalance in the protrusion is also reduced because the protrusion is located near the center spindle hole.
The clamping method of an optical data recording medium according to the present invention holds the optical data recording medium in a clamping area on either or both sides of the protrusion. The optical data recording medium can therefore be held and spun stably during recording and playback, assuring consistent recording and playback and good signal quality.
The optical data recording medium manufacturing method of this invention can also easily form the protrusion, thus improving optical data recording medium productivity.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
The present invention will become readily understood from the following description of preferred embodiments thereof made with reference to the accompanying drawings, in which like parts are designated by like reference numeral, and in which:
Preferred embodiments of the present invention are described below with reference to the accompanying figures.
Embodiment 1
The outside diameter of this optical data recording medium 110 is 120 mm. The clamping area CA is the area where the optical data recording medium 110 is clamped and held when reading and/or writing data to the signal recording layer 103. The inside diameter DCAI of the clamping area CA is 22 mm and the outside diameter DCAO is 33 mm.
A transparent protective layer 102 protects the signal recording layer 103. A light beam with a 405 nm wavelength, for example, is emitted from an optical head through the transparent protective layer 102 and focused on the signal recording layer 103 for reading and/or writing data.
The transparent protective layer 102 is, for example, 100 μm thick. The signal recording layer 103 is formed over signal pits or grooves that are formed in the signal area SA of the signal substrate 104. The inside diameter DSAI of the signal area SA is 42 mm and the outside diameter DSAO is 119 mm. The signal recording layer 103 could be a multilayer film including a GeSbTe phase-change film, a multilayer film including a pigment film, or a metal alloy thin film.
The diameter Dc of the spindle hole 101 is 15 mm. The inside diameter Dti of the protrusion 100 is 18 mm, the width in the radial direction (radial width) is 1 mm, and the height of the protrusion 100 above the surface of transparent protective layer 102 is 0.3 mm. The radial width of the protrusion 100 is preferably 0.2 mm to 1 mm. A width of 0.2 mm or greater is preferred to assure sufficient mechanical strength.
The height of the protrusion 100 from the surface of transparent protective layer 102 is preferably 0.1 mm to 0.5 mm. If the height of the protrusion 100 is at least 0.1 mm above the surface of the transparent protective layer 102 and the transparent protective layer 102 is placed on a flat surface with the protrusion 100 facing down, the transparent protective layer 102 will not contact the flat surface and will be protected from scratching.
Furthermore, while the inside diameter Dti of the protrusion 100 is 18 mm, the inside edge of the protrusion 100 must only be separated at least 0.1 mm from the outside edge of the spindle hole 101. In other words, the inside diameter of protrusion 100 must be greater than diameter (DC+0.2) mm and the outside diameter must be less than inside diameter DCAI of the clamping area CA. If inside diameter Dti is greater than (DC+0.2) mm, the disc can be stably clamped and spun, assuring good signal quality, during recording and playback without interference between the centering cone of the recorder or playback device and the protrusion 100.
Table 1 shows the effect of the protrusion 100 at different elevations from the surface of the transparent protective layer 102. The indices used to evaluate the effectiveness of the protrusion 100 were the amount of scratching on the surface of the transparent protective layer 102, and the ease with which the disc 110 can be picked up, when placed with the transparent protective layer 102 face down against a flat surface.
TABLE 1
Protrusion height and effect
Height (mm) of protrusion from
transparent protective layer surface
0
0.05
0.1
0.2
0.3
0.4
0.5
Surface scratching
NG
Some
OK
OK
OK
OK
None
Ease of pickup
NG
Poor
Poor
Good
Good
Very
Very
good
good
When the height of the protrusion 100 is 0 mm from the surface of the transparent protective layer 102, that is, when there is no protrusion 100, there is excessive scratching of the transparent protective layer and it is difficult to pick the disc up off a flat surface. While a protrusion height of only 0.05 mm provides a slight improvement in scratching and ease of picking up the disc, the protective margin is still not sufficient and the surface of the transparent protective layer must be treated in some way, such as by hardening, to improve scratch resistance.
A protrusion height of 0.1 mm provides a significant improvement in scratching, that is, there is substantially no scratching. When the protrusion height is 0.2 mm to 0.3 mm there is essentially no scratching of the transparent protective layer and the disc is easy to pick up.
When the protrusion height is 0.4 mm there is essentially no scratching of the transparent protective layer and the disc is very easy to pick up. With a protrusion height of 0.5 mm no scratches were found in the transparent protective layer surface and the disc was very easy to pick up.
Increasing the height of the protrusion 100 to greater than 0.5 mm above the surface of the transparent protective layer does not yield any improvement in scratch protection or ease of picking the disc up. Furthermore, a height greater than 0.5 mm increases the amount and therefore the cost of the required materials, and is therefore not desirable.
It should be noted that if the diameter DC of spindle hole 101 is approximately 15 mm, the diameter of the protrusion 100 is between 17.5 mm to 22 mm, and the height of the protrusion 100 from the surface of transparent protective layer 102 is 0.3 mm or less, the three benefits described below, which include the effects noted above, can be achieved. (Note that (2) and (3) below are the effects described above.)
(1) The protrusion 100 does not interfere with the chuck used to clamp the disc during recording and playback of the optical disc.
(2) Scratches in the transparent protective layer 102 can be prevented whether the disc is warped or placed on a flat surface.
(3) The disc can be easily picked up from a flat surface even if the disc is warped.
Item (1) above is described first.
As shown in
This results in the optical data recording medium 110 being clamped by the chuck 1200 as shown in
Furthermore, because the inside diameter of the clamping area in a conventional optical disc such as DVD media is also 22 mm, interference between the protrusion 100 and the jaws and chucking surface of the chuck can be prevented even if the optical data recording medium 110 is accidentally chucked using a chuck for conventional DVD media.
If the protrusion 100 is located in a circumferential band with a 17.5 mm inside diameter and 22 mm outside diameter when the diameter DC of the spindle hole 101 is approximately 15 mm, it is therefore possible to avoid interference between the protrusion 100 and chuck 1200, including the jaws 1201, even when using a simple chuck 1200 of the type that applies the greatest chucking force to the optical data recording medium 110.
Items (2) and (3) are described above with reference to Table 1, and are described in further detail below with reference to
When someone then attempts to pick up the disc 110, the increased contact area between the fingers and the outside edge E of the disc 110 makes it easier to pick the disc 110 up.
The surface of the transparent protective layer 102 is also protected from scratches due to contact with the surface P because it does not touch the surface P.
The height of the protrusion 100 above the surface of the transparent protective layer 102 can be determined according to the warpage allowed in the optical data recording medium 110. When the maximum allowed warpage in the optical data recording medium 110 is 0.35 degree as in this example, however, a protrusion height of 0.3 mm or less above the surface of the transparent protective layer 102 is sufficient to achieve the benefits described above.
To assure that the height of protrusion 1400 from the surface of the transparent protective layer 102 is 0.3 mm or less as shown in
Furthermore, to prevent interference of the protrusion 1400 with the chucking surface 1203 and chuck 1200 better than the example shown in
Furthermore, if the disc is not greatly warped as shown in
Examples of the shape of the protrusion when seen in a top view are shown in
The broken ring configuration shown in
When multiple discrete protrusions are disposed with a configuration such as shown in
Furthermore, the shape of the protrusion(s) when seen in plan view shall not be limited to those shown in
Tt=Ttcv+(transparent protective layer thickness)
where Ttcv is the height above the surface of the transparent protective layer 402. In this example Ttcv is 0.1 mm to 0.5 mm.
It is also possible for the transparent protective layer to not be formed in the clamping area CA.
The effect of disposing a protrusion projecting from the surface of the transparent protective layer on the light incidence side of the area between the spindle hole and clamping area of the optical data recording medium is described next.
The protrusions cannot be disposed to any desired place on the optical disc, and more specifically must be disposed where there will be no contact between the protrusions and the optical head. With the optical data recording medium according to a first embodiment of the invention the protrusions are disposed in the area between the spindle hole and clamping area CA. When reading and/or writing data to the signal recording layer the optical head is always on the outside circumference side of the clamping area CA. As a result, there is no contact between the optical head and the protrusions, which are on the inside circumference side of the clamping area CA and separated from the optical head by the clamping area CA.
A method of manufacturing these protrusions according to the present invention is shown in
A pair of dies 500 is prepared and a stamper 501 is set in one die as shown in
The mold 500 is then closed as shown in
The material for bonding the protrusions 600 can be precoated to the part of the protrusions 600 that will touch the protrusion-less disc 601. Alternatively, the part touching the protrusion-less disc 601 could be heated and melted for bonding. The protrusions 600 could even be metal. Using the method shown in
Protrusions can also be formed from a liquid resin using a screen printing process. In this case a printing screen is formed with the desired shape of the protrusions, and the liquid resin is screen-printed onto the disc surface. Because the method shown in
As described above, an optical data recording medium according to this first embodiment of the invention has one or more protrusions located on the surface between the inside circumference of the clamping area CA and the outside edge of the spindle hole, assuring that the protrusions will not contact the optical head during recording or playback.
Furthermore, surface scratches can be prevented even when the disc is placed on a flat surface with the transparent protective layer side facing down because the protrusions assure that the transparent protective layer is sufficiently above and does not contact the flat surface.
Yet further, the proximity of the protrusions to the spindle hole minimizes the effect of any weight imbalance in the protrusion part. A stable, high quality signal can therefore be achieved.
Embodiment 2
When recording or playing a high density optical disc with a 0.1 mm thick transparent protective layer on the laser incidence side (the read/write side) of the disc using a 0.7 to 0.9 NA optical head, such as a high 0.85 NA optical head, the distance between the optical head and the high density optical disc, known as the working distance WD, is generally very small, typically 0.1 to 0.4 mm. A working distance WD of 0.4 mm or less is recommended, for example, in ISO M 2002 Technical Digest ThB.1 published by the International Symposium on Optical Memory.
Because of the short working distance WD in this case, the optical head can easily strike the transparent protective layer of the disc when the focusing servo is disrupted by such external factors as vibration of the disc surface. The high NA used with high density optical discs means that dust on the surface of the transparent protective layer can easily disrupt the focusing servo. When the focusing servo is off track, the optical head can easily collide with the protrusion on the disc surface. To prevent this, a shield for protecting the lens is required on the surface of the optical head. The thickness of this shield (approximately 0.1 mm) further decreases the working distance to 0.3 mm or less. If the working distance of the optical head increases, the outside diameter of the lens also increases. The outside diameter f of a lens with a 0.4 mm working distance is 6 mm to 8 mm (including the lens holder).
When reading and/or writing the signal area with inside diameter DSAI as shown in
The height Ttcv of this protrusion 800 is considered next.
The closer protrusion 800 gets to inside diameter DSAI, the closer protrusion 800 gets to the lens holder 900. The height Ttcv must therefore be lowered. Furthermore, because the outside diameter Dto of protrusion 800 is 35 mm, there is 3.5 mm to inside diameter DSAI (=42 mm). If the actual working distance WD of the lens is 0.2 mm, there is 0.5 mm of space between the lens holder 900 and protrusion 800 because the radius R of the lens holder is approximately 3 mm. Radius R is approximately 4 mm if the working distance WD is 0.3 mm, but because height Ttcv is 0.25 mm, the protrusion 800 will not collide with the lens holder 900.
It is thus necessary to consider the working distance WD of the lens when the protrusion is located in the area between clamping area CA and signal area SA. However, if the height Ttcv of the protrusion is 0.1 m to 0.3 mm, the protrusion 800 will not collide with the lens holder 900.
It will also be obvious that the surface protection performance of the transparent protective layer is also achieved.
It should be noted that the protrusion can be located in the area between the clamping area CA and signal area SA as described in this second embodiment of the invention whether the transparent protective layer is not formed in the clamping area CA as shown in
The protrusion in this second embodiment can also be manufactured using the same materials and methods described in the first embodiment. Note that depending upon the inside diameter of the stamper, it may be necessary to provide a cavity in the stamper with the injection molding method shown in
The shape and configuration of the protrusion can be the same as described in the first embodiment above. When the protrusion is in an area between the clamping area CA and signal area SA as described in this second embodiment of the invention, and particularly when the protrusion is within 2 mm on the outside circumference side of the clamping area CA, collision of the optical head with the protrusion can be prevented during both recording and playback, and surface scratches can be prevented even when the optical data recording medium is placed on a flat surface with the transparent protective layer of the disc facing the flat surface because the protrusion assures that the surface of the disc does not contact the surface on which it is placed.
Embodiment 3
An optical data recording medium in which the protrusion is located in the clamping area CA is shown in
The inside diameter Dti and outside diameter Dto of the protrusion 1100 are defined by the following relation.
DCAI<=Dti<Dto<=DCAO
This configuration also prevents scratching when the optical data recording medium 1110 is placed on a flat surface with the transparent protective layer 1102 facing the flat surface because the protrusion assures a sufficient gap between the transparent protective layer 1102 and said flat surface.
Collision of the optical head with the protrusion is also prevented because the optical head does not enter the clamping area CA.
Note that the thickness of the transparent protective layer, inside diameter DCAI, and outside diameter DCAO are the same in this embodiment as in the first embodiment.
The width of the protrusion 1100 and the height of the protrusion from the surface of the transparent protective layer 1102 are also the same as in the first embodiment, that is, in the ranges 0.2 mm to 1 mm, and 0.1 mm to 0.5 mm, respectively.
Unlike in the first and second embodiments, the disc drive clamps the optical data recording medium 1110 on both sides of the protrusion 1100 in this third embodiment. This is possible except when DCAI=Dti or Dto=DCAO.
In the example shown in
In the example shown in
The optical data recording medium can be held stable and rotated with sufficient pressure during both recording and playback to assure good signal quality and reliable recording and playback performance.
It should be noted that the disc is clamped on both sides of the protrusion 1100 in this embodiment, but it could be held only in the area between inside diameter DCAI and the inside circumference edge of the protrusion 1100, or the area between outside diameter DCAO and the outside circumference edge of the protrusion 1100.
While this third embodiment has been described with reference to the configuration shown in
The protrusion 1100 of this third embodiment can also be formed using the same materials and methods described in the first and second embodiments above.
The shape and configuration of the protrusion could also be as described in the first embodiment.
Clamping an optical data recording medium according to the present invention shall not be limited to holding the disc with chucking jaws in the clamping area CA on only one side of the disc as shown in
The material used to manufacture the signal substrate is not particularly discussed in the above-described embodiments, but is preferably a plastic such as polycarbonate, norbornene resin, or polyolefin resin.
The transparent protective layer can also be formed by applying a sheet film thinner than the desired thickness with adhesive, or applying a coat of liquid resin. When a thin sheet film is applied with adhesive, the adhesive could be a UV-cure resin, thermosetting resin, or pressure sensitive adhesive, for example.
When a coat of liquid resin is applied, the resin could be a UV-cure resin or thermosetting resin, for example.
Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.
Hayashi, Kazuhiro, Mohri, Masanari, Ohno, Eiji
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